Field Notes On The Nikau

Rhopalostylis sapida by any other name. Peter Richardson and Stephen Powell contribute two sides of the same coin.
Peter Richardson, Advanced Technologies Ltd., Science Park, Cambridge, U.K.
Chamaerops No. 7, published online 23-10-2002

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The Shaving Brush Palm (Rhopalostylis sapida) in habitat.

My second trip to New Zealand, in March, to collect seed in tracts of native bush in the northern half of the North Island, gave me plenty of opportunity to get to know the Nikau Palm (Rhopalostylis sapida) in the native habitat It's a favourite warm-temperate palm of mine because the crownshaft and clean, ringed trunk give it a decidedly tropical look in contrast to the phoenicoid and coryphoid warm-temperate palms of the northern hemisphere with their persistent leaf bases and matted fibres. And it is used to maritime westerly winds like those that dominate the British climate.

Native-plant buffs in New Zealand claim there are regional forms of the Nikau of varying stoutness and crown shapes. However, the areas I covered were limited to the northern, subtropical zone and yet I saw all shapes and sizes of palm, the differences seeming to reflect the age of the plants, vigour and illumination. Their size I found extremely variable according to the site. Trunked plants can have leaves as short as 120 cm or up to 4m long. Correspondingly, the trunks varied from 12-22cm in diameter. Lush plants that had put height on fast in their youth had internodes up to 4cm wide, and they stay green in shade. In the case of a 20cm diameter tree with 4cm internodes, the tree is adding a solid cylinder of trunk of volume 1.25 litres to itself with each leaf produced. Higher up the trunks of mature plants the internodes become narrower until one leafscar is touching the next.

The narrowest, most columnar crowns belong to very vigorous adolescent to young-adult trees in some shade. Very deep shade causes most plants to adopt a more lax shape. Direct sun stimulates a stiff shuttlecock shape, the margins of the pinnae rolled back in a curl, with the outer leaves characteristically tattered and burnt at the tips in all but the most sheltered and humid spots. The most perfect plants are found in windless deep shade, usually in gully bottoms, and there look rather like the Nikau's Australian relative, Archontophoenix cunninghamii. They are extremely slow growing; maybe only one or two leaves a year, in these conditions. Fortunately, their general hard, leatheriness makes them unpalatable to herbivores generally, and even the voracious possums leave them alone.

As far as reproduction is concerned, plants in the North seem not to observe the seasons saw panicles at all stages of development from still being sheathed, through flowering to bearing ripe red berries. Berries are abundant, falling to the ground at the base of the trunk or the flesh eaten and the seed dropped by birds. Either way the seeds don't travel far and hence the Nikau often lives in groves. Plants with their crowns in sun reproduce the most, and can have three panicles at different stages of development at once.

The Nikau will grow exposed to sea winds on the west coast, but gets severely tattered. This does not seem to be a problem to them as they grow, fruit and regenerate (where grazing pressure allows) freely despite looking an awful mess. Most specimens in New Zealand gardens are tatty and yellow, because they are in direct sun, with dry soil and wind exposure. They also look tattered at their altitudinal limit of around 500 metres in the Coromandel Ranges, where there is at least some frost in the winter.

Unfortunately they are not very hardy in the European sense, and, to grow good specimens in Britain means pampering them in a warm greenhouse. My six plants are OK outside in Cambridge all year except in frost, but each new leaf is then barely bigger that the previous one. Warm indoor nights in particular result in noticeably freer growth.

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